Latchable track assemblies are very widely used to retain a vehicle seat in slidably movable yet selectively positionable relation to a vehicle floor pan, such latchable track assemblies typically comprising first and second slidably engaged track members interfaced one to the other by a plurality of ball bearings, with the first track member being fixed with respect to the vehicle and the second track member being fixed with respect to the seat. An example of such a prior art latchable track assembly is shown in U.S. Pat. No. 4,863,289 (Lecerf) issued Sep. 5, 1989.
It is common in the prior art to use a latching mechanism to selectively lock the two track members from slidably moving with respect to each other. Such a latching mechanism is typically rigidly attached to the second track member, which track member is fixed to the vehicle seat, thereby to provide consistent access to a handle means by the seat occupant. The latching mechanism typically comprises a bracket member and an elongated locking lever, with the locking lever being pivotally mounted on the bracket member adjacent its midpoint. The locking lever, which includes the handle means as an integral portion at one end, is pivotally mounted as aforesaid about a generally vertical axis, and has a small row of horizontally protruding detent members, usually two or three in number, that are selectively moved by corresponding movement of the handle means in an arc about the generally vertical axis into and out of the interstices between the consecutive teeth that form a row of teeth on the first track member, thereby providing for selective locking the two track members with respect to each other.
Such prior art latch mechanisms are rather bulky in their construction, with the locking lever requiring a significant amount of available free-space for operative movement between the locked and unlocked configurations of the mechanisms. This significantly limits the design applications in which such prior art track latching assemblies can be used.
It has been found that such prior art track latching mechanisms employing a pivotally operable locking lever can only accommodate a maximum of about three detent portions and still operate smoothly and properly in terms of being positioned into and removed from the aforesaid interstices between the teeth of the first track member. This is so because the detent portions must fit in close locking relation between the teeth of the first track member, but must also travel in a radius arc when being moved into or out of the interstices, which tends to cause jamming of the detent portions in the interstices if the arc is unduly large, as where more than about three detent portions are positioned seriatim along the locking lever. It is, however, desirable, to have a latching mechanism that is pivotally operable for reasons of simplicity of design, ease of use, reliability, and low manufacturing costs.
Known latching mechanisms having only three or less detent portions are known to sometimes fail, by breaking under the extreme shearing forces caused by the rapid acceleration or deceleration of a vehicle under crash or crash-like conditions. Such failure of the latching mechanism results in the vehicle seat sliding freely in the vehicle seat track assembly, which can cause undue injury to a seat occupant or to other occupants of the vehicle. Such latching mechanism failure has become more pronounced in view of the recent design trend, dictated by safety and convenience considerations, of mounting the female portion of the seat-belt harness or, indeed, both the male and female portions of the seat-belt harness, onto the vehicle seat frame. Such mounting of the seat-belt harness components means that the crash loads previously transferred by the seat-belt harness to structural components of the vehicle body are instead borne by the vehicle seat frame. Not only must the seat frame itself be made more robust to safely accommodate this increased loading, but so also must the seat track latching mechanisms. For this reason, prior art seat track latching mechanisms, and particularly those limited by their inherent geometry to three or less detent portions, have proven unsuitable for such seat-belt loading applications.
A further problem with known prior art latching mechanisms is that, where the latching mechanism becomes detached from the second track assembly, such as might happen during an impact to the bracket member holding the locking lever, there is no longer a physical interconnection between the second track member and the first track member. Resultingly, the first track member and the second track member are no longer precluded from slidably moving with respect to one another, which is, of course, dangerous to the vehicle's occupants.
Perhaps most importantly, known prior art latchable track assemblies have teeth and/or detent portions that are not enclosed by the track members at all times, and are thus exposed to the ambient vicinity of the track assembly. This potentially creates a problem in that upholstery material of the seat, carpet material of the vehicle, detritus or even stray articles under the seat, could interfere with the intended operation of the latching mechanism, thereby creating a safety hazard to the seat and vehicle occupants. Moreover, grease or other lubricant present on the track assembly and the latching mechanism can contact the vehicle carpet material etc., or the hands of the seat occupant, thereby soiling same.